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POLYURETHANES in RIGID and FLEXIBLE ELECTRONICS NOVEL HYBRID PROCESSING TECHNIQUES and REAL-TIME MONITORING OF MATERIAL PROPERTIES

Nugay, Isik Isil

Abstract Details

2014, Doctor of Philosophy, University of Akron, Polymer Engineering.
Bistable liquid crystal displays are multilayer devices composed of external layers of flexible conductive film typically biaxially stretched PET and highly compressible interior phase separated droplets of liquid crystal (90+%) dispersed in an thermosetting polymer. The objective of this research was to reach a fundamental understanding of the thermo-mechanical behavior of this display and its individual layers while a polyurethane lens encapsulation is applied on both sides using insert injection molding. In this process the display undergoes spatio-temporally varying heating and cooling that causes considerable problems including thermal expansion, shrinkage and compression of individual layers. To address these, we have developed an instrumented insert injection mold to monitor the temperature and pressure development during the course of insert injection molding. As the encapsulation layers, low viscosity and low melting polyurethane material was selected to avoid operating the machine at too high temperature and pressures. Flow simulation aids were also utilized and compared to experimental results to validate tool usage for the optimization of similar encapsulation applications. Final study on this thesis is the real-time mechano-optical and segment specific orientation properties thermoplastic polyurethane(urea) films and different soft segment length effects. While the introduced film-insert injection compression molding process for encapsulation of cholesteric liquid crystal displays with flexible and rigid lenses replaces the PSA-lens or cover glass lamination technique that fails to fully protect the display parts, still remains complex and requires optimization of multiple process conditions. Process monitoring instrumentation on newly designed and constructed interchangeable cavity hot runner mold allowed addressing development challenges arising from an insert multilayer display with 90+% liquid crystal content as well as different thermal expansion coefficients between the layers and the lens material with delamination and warpage potential. Display substrate material selection criteria for lowered warpage were defined with supporting thermal characterizations and controlled shrinkage on PET films were reported as a separate chapter. During proposed lens encapsulation, the pressure changes were evaluated with screw and mold movements using position detection via displacement transducers attached to track the mold closure and screw forward motion. Among the process parameters, tested also by applying the design of experiments with Taguchi method, mold temperature was found to be the most influential parameter on warpage, followed by pin gate opening time, packing pressure, and cooling time. Flexible display substrate encapsulation flow simulations are completed in Moldex3D R12 software to help pre-visualize the changing process parameters affecting part quality. Part frozen layer formation and birefringence development were also discussed. The experimental and simulation results for temperature and pressure profiles as well as melt front were found to be in good agreement. Multi-component injection compression molding module of Moldex3D was used an effective tool to avoid trial-and- error method experiments. In order to understand the thermo-mechanical behavior of the electrode PET layers, real-time optical properties during biaxial stretching and heat setting of PET films were investigated to elucidate its shrinkage behavior during heating/cooling cycle. The samples with tightly ordered entanglements in specific direction shrunk higher along that direction to relax when subjected to heating. The relaxation of ordered unstable structure and re-crystallization were possible via heat setting which reduced shrinkage values. The optimum samples with reduced final and maximum shrinkage/expansion values as well as MD to TD variations were obtained by using 3x1 UCW stretched and heat set at 190°C for different time frames. Finally, real-time segment specific rheo-optical properties during stretching and relaxation of three polyurethane(urea)s (PUU) grades with hard segments consisting of bis(4-isocyanatocyclohexyl)methane (HMDI) and 2-methyl-1,5-diaminopentane (MDAP) and soft segments consisting of poly(ethylene oxide) (PEO) oligomers were investigated. All PUUs had 30% by weight hard segment content. Three different molecular weight PEO oligomers were used for synthesis resulting in soft segment length variation among samples. Low molecular weight PEO based PUUs have shown phase mixing whereas, mid and high molecular weight PEO based ones phase segregation of hard and soft segments in AFM studies. Each grade exhibited different rheo-optical behavior consisting of multiple regimes discussed in detail and shown in model. The initial morphology governed the segment specific orientation at low and high strain values. Co-continuous structures resulted in similar hard and soft segment response even at lower strain levels and relaxation stage resulted in strain induced reorientation of soft-segments. Whereas, for the phase segregated structures, soft segment orientation was found at low strain levels. Later, the connection with the hard segments has driven orientation in chain axis towards the stretching direction marked by the rheo-optical behavior change from high strain-optical constant to lower strain-optical constant.
Mukerrem Cakmak, Dr. (Advisor)
David Simmons, Dr. (Committee Member)
Karim Alamgir, Dr. (Committee Member)
Darrell Reneker, Dr. (Committee Member)
Chrys Wesdemiotis, Dr. (Committee Member)
244 p.

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Citations

  • Nugay, I. I. (2014). POLYURETHANES in RIGID and FLEXIBLE ELECTRONICS NOVEL HYBRID PROCESSING TECHNIQUES and REAL-TIME MONITORING OF MATERIAL PROPERTIES [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1406633847

    APA Style (7th edition)

  • Nugay, Isik. POLYURETHANES in RIGID and FLEXIBLE ELECTRONICS NOVEL HYBRID PROCESSING TECHNIQUES and REAL-TIME MONITORING OF MATERIAL PROPERTIES. 2014. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1406633847.

    MLA Style (8th edition)

  • Nugay, Isik. "POLYURETHANES in RIGID and FLEXIBLE ELECTRONICS NOVEL HYBRID PROCESSING TECHNIQUES and REAL-TIME MONITORING OF MATERIAL PROPERTIES." Doctoral dissertation, University of Akron, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1406633847

    Chicago Manual of Style (17th edition)